A charged particle beam apparatus represented by a scanning electron microscope (SEM) detects charged particles (secondary electrons or the like) obtained by scanning a sample with a charged particle beam such as an electron beam and forms an image. Particularly, in an SEM that measures and inspects a semiconductor, electrons generated from a sample through electron beam irradiation are detected and thereby, the shape or composition of the sample is measured or a defect in an LSI is inspected.
In order to improve the yield ratio of a three-dimensional device, three-dimensional observation is required as an important function in an inspection instrument and a measuring instrument which use electron beams. The three-dimensional observation in the SEM is performed using a method in which a stage is tilted and an image is obtained. However, the tilt of the sample stage or column requires a mechanical operation and thus, there is a problem in that reproducibility of a throughput or a tilted angle deteriorates.
In order to perform the three-dimensional observation without a mechanical tilt, a method in which a deflector is used to tilt a beam is considered. However, when the deflector is used to tilt (deflect) the beam, an off-axis aberration of a lens occurs, the beam is increased in diameter, and resolution deteriorates particularly due to an off-axis chromatic aberration and a deflected coma aberration. In order to correct the off-axis aberrations which occur during the beam tilt, aberrations having reverse signs, which are equal to the aberrations occurring in an objective lens need to be generated in a separate optical element and thus, the following method is known.
PTL 1 discloses an adjustment method in which an optical condition is set to achieve a positional shift of zero on an image when an applied voltage and an excitation current to respective lenses are changed and thereby an off-axis chromatic aberration of an objective lens is corrected.
PTL 2 discloses a scanning-type electron microscope which is aimed at achieving stereoscopic observation without a positional shift on the sample even when a beam is tilted. PTL 2 shows an effectivity of forming a support point of deflection of a central trajectory (deflected trajectory) which is curved by a deflector at the same position of an object plane of a lens.
PTL 3 discloses a method in which electromagnetic multipoles are used to generate chromatic dispersion and thereby, an off-axis chromatic aberration which occurs during a beam tilt is corrected. Further, PTL 4 discloses a method in which a beam is tilted without moving an object point of an aberration corrector disposed to be closer to an electron source than an objective lens and thereby, a chromatic aberration and a spherical aberration which occur during a beam tilt are corrected by the aberration corrector.